Paper strength improver and paper obtained by using the paper strength improver

[Purpose] The purpose of the invention is to provide an acrylamide-based paper strength improver and a manufacturing method thereof, even in the condition that paper is made by using paper pulp with conductivity short of 3 mS/cm and in the condition that paper is made by using paper pulp with conductivity more than 3 mS/cm, the acrylamide-based paper strength improver has excellent retention on the paper pulp and further has high agglutination on the paper pulp, and the obtained paper has food characteristics and shows high paper strength improving effect. [Solution] The paper strength improver is characterized in that the paper strength improver has an amphiprotic (methyl) acrylamide-based water-soluble polymer having 7-30 mass% solid component, weight-average molecular weight of the amphiprotic (methyl) acrylamide-based water-soluble polymer is 1,600,000-10,000,000, after attenuated by using water having conductivity of 4 mS/cm measured at 25 DEG C which is obtained by mixing deionized water with sodium sulfate, turbidity distribution of the 1 mass% aqueous solution of the amphiprotic (methyl) acrylamide-based water-soluble polymer between pH3-9 has a maximum value, and the maximum value is 15-2,000 NTU.